It is known to blow mold containers such as, for example, beverage bottles from preforms. Preforms may be produced by various molding technologies and processes such as, for example, injection or compression molding.
One such prior art preform is depicted with reference to FIG. 1. In particular, there is depicted an original preform 100 that is blow moldable to form a container (not shown). The original preform 100 has a hollow tubular body that includes a neck finish 102 at an open end thereof, an original base 106 at a closed end thereof and a body 104 arranged between the neck finish 102 and the original base 106. The neck finish 102 is configured to retain, in use, a closure (not shown) thereon, and the body 104 and the original base 106 are blow moldable to form corresponding parts of the container.
The original preform 100 may be molded in a mold stack of an injection mold (not shown) such as, for example, the mold stack 520 shown in FIG. 5. The mold stack 520 has various stack components including a core assembly 522 (i.e. core insert 524 and lock ring 523), neck rings 526, a cavity insert 528 and a gate insert 530 that are configured to cooperate together to define a molding cavity 532. In use, molding material is injected into the molding cavity 532; via a gate passage that is defined in the gate insert 530, to form the original preform 100 therein. The interface between mating stack components of the mold stack 520 defines a “split line”. Two of the more prominent split lines are identified in FIGS. 1 and 5 as including a base split line S1 and a neck split line S2. As its name implies, the base split line S1 defines a transition between the body 104 and the original base 106 of the original preform 100, the foregoing being defined at the interface between the cavity insert 528 and the gate insert 530. Likewise, the neck split line S2 defines a transition between the body 104 and the neck finish 102 of the original preform 100, the foregoing being defined between the cavity insert 528 and the neck rings 526.
To reduce an amount of molding material in the preform, and thus the container blow molded therefrom, it is known to remove molding material from a base of the preform with a reshaping thereof. An example of the foregoing may be appreciated with reference to FIG. 2. In this example the original base 106 of the original preform 100 is replaced by a lighter weight base 206. In particular, an outer base surface 207 of the lighter weight base 206 replaces a hemispherical outer base surface of the original base 106. The outer base surface 207 of the converted base includes compound surfaces 207A, 207B, 207C of different curvature that fit within the original outer body surface 107. The outer base surface 207 is furthermore defined to join with an outer body surface 103 (FIG. 1) of the body 104 at the base split-line S1 of the original base 106 and to intersect with a longitudinal axis X of the original preform 100 at a common point NI to the original outer body surface 107 (disregarding any gate vestige 108, 208). In so doing molding material is taken away from a wall of the base in a central part of the base without changing a total length TL (FIG. 1) of the preform 100, 200.